Some vehicle engine systems utilize gasoline direct injection (GDI) to increase power efficiency and range over which the fuel can be delivered to the cylinder. GDI fuel injectors may demand fuel at higher pressure for direct injection to create enhanced atomization providing more efficient combustion. In one example, a GDI system can utilize an electrically driven lower pressure pump (also termed a fuel lift pump) and a mechanically driven higher pressure pump (also termed a direct injection fuel pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications the higher pressure fuel pump may be used to increase the pressure of fuel delivered to the fuel injectors. The higher pressure fuel pump may include a solenoid actuated “spill valve” (SV) or fuel volume regulator (FVR) that may be actuated to control flow of fuel into the higher pressure fuel pump.
Various control strategies exist for operating the higher and lower pressure pumps to ensure efficient fuel system and engine operation. One strategy for reducing consumption of electrical energy in the higher pressure pump may include energizing the solenoid actuated spill valve for shorter durations. For example, a normally-open solenoid actuated spill valve may be energized to close at a certain time during a compression stroke of the fuel pump based on a desired fuel volume output. The solenoid actuated spill valve may then be de-energized when pressure within a compression chamber of the higher pressure fuel pump increases sufficiently. Herein, the increase in pressure within the compression chamber may be adequate to maintain the spill valve in its closed position even though the solenoid is de-energized. As such, the solenoid actuated spill valve may be de-energized at an earlier time, e.g. before the compression stroke is completed, enabling a reduction in energy consumption and solenoid heating.
However, the inventors herein have identified a potential issue with the above strategy. As an example, the strategy of de-energizing the solenoid actuated spill valve at an earlier time may be ineffective when fuel vapor is present at an inlet of the direct injection fuel pump. If fuel vapor is at least partially ingested during pumping, pressure within the compression chamber of the direct injection fuel pump may not be sufficient to hold the spill valve closed after the solenoid actuated spill valve is de-energized. Accordingly, de-energizing the solenoid at the earlier time may result in a decrease in compression pressure due to fuel flow out of the compression chamber via the spill valve. Pump efficacy may be reduced and the desired output of fuel volume, at a desired fuel pressure may not be achieved. The inventors herein have recognized that control strategies are needed that specifically address situations when fuel vapor is present at the inlet of the higher pressure direct injection fuel pump.
Thus in one example, the above issue may be at least partially addressed by a method, comprising energizing a solenoid spill valve of a direct injection fuel pump for an angle past top center of a piston in the direct injection fuel pump. The angle may be a non-zero angle and may result in the valve being energized longer than a minimum angular duration past top center of a position of a piston in the direct injection fuel pump in response to fuel vapor detected at an inlet of the direct injection fuel pump. In this way, pump efficiency may be maintained during conditions when fuel vapor is present at the inlet of the higher pressure (or direct injection) fuel pump.
For example, a fuel system in a GDI engine may include a lift pump positioned upstream of a direct injection fuel pump. A fuel composition sensor may be positioned downstream of the lift pump and upstream of the direct injection fuel pump. A volume of fuel pumped by the direct injection fuel pump may be controlled by an angular duration of energizing a solenoid actuated spill valve in the direct injection fuel pump. During conditions when fuel vapor is not detected at an inlet of the direct injection fuel pump, the solenoid actuated spill valve may be energized within a compression stroke for a shorter angular duration. Herein, the solenoid actuated spill valve may be de-energized prior to a completion of the compression stroke in the direct injection fuel pump. Fuel vapor may be detected based on fuel capacitance as measured by the fuel composition sensor. When fuel vapor is detected at the inlet of the direct injection fuel pump, the solenoid actuated spill valve may be energized for at least a minimum angular duration based on the position of a piston in the direct injection fuel pump. In another example, if fuel vapor is present, the solenoid actuated spill valve may be energized for longer than the minimum angular duration based on the position of the piston in the direct injection fuel pump. As such, the solenoid actuated spill valve may be energized at least until after the compression stroke is completed when fuel vapor is detected at the inlet of the direct injection fuel pump.
In this way, the solenoid actuated spill valve may be controlled differently based on presence of fuel vapor at the inlet of the direct injection fuel pump. By energizing the solenoid actuated spill valve for at least a minimum angular duration based on the position of the piston of the direct injection fuel pump, closure of the spill valve may be ensured throughout the compression stroke of the pump. Overall, fuel pump efficacy may be maintained to provide a commanded fuel volume at a desired fuel pressure to direct injectors.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.